Elongated medical devices such as catheters are used in a wide variety of medical procedures. Many of these procedures require fluid transfer, for example from one portion of a patient's body to another, from outside to inside the patient, or for removal of fluids from a patient's body. Examples of such therapeutic procedures include infusion or irrigation, aspiration of bodily fluids, and perfusion, along with many other procedures that benefit from fluid communication through a medical device.
Some fluid transfer procedures involve the use of balloon catheters. Balloon catheters are used to perform angioplasty, for temporarily blocking blood vessels, and for deploying stents, among other uses. In order to facilitate inflation and deflation of the balloon, balloon catheters typically have the ability to transport fluids to and from the balloon, often through a fluid flow lumen.
In addition, many intracorporeal procedures require devices to travel significant lengths through tortuous pathways in a patient's body. Such applications require the catheter shaft to have both strength and flexibility. A catheter shaft can be subjected to many different forces: for example, axial or torsional, or other forces that can cause the shaft to bend and/or kink. Catheters with fluid flow lumens are often subject to all of these forces while also being used for fluid transfer.
Medical devices with fluid flow lumens often comprise an inner and an outer member. In order to provide for a stronger shaft, some designs have used inner members with larger outer diameters. This can add overall strength to the shaft (thicker shaft walls can lead to higher strength) and can also make the clearance between the inner surface of the outer member and the outer surface of the inner member smaller. When forces act on such a shaft design, the inner member can come in contact with the outer member, and the two members together can yield more shaft strength and resistance to kinking than either member might separately provide. With less clearance between the inner and outer members, less relative movement is required to cause them to come into contact, thus providing a shaft that can be strong and kink resistant. However, designs in which the outer diameter of the inner member is made larger can cause a blockage or restriction of the fluid flow lumen, eliminating or restricting the ability to transfer fluids through the shaft.